ENHANCEMENT OF TROPICAL OCEAN EVAPORATION AND SENSIBLE HEAT-FLUX BY ATMOSPHERIC MESOSCALE SYSTEMS

The enhancement of monthly averaged evaporation by atmospheric mesosca le systems is estimated from longterm hourly observations of surface m eteorological data from the Tropical Ocean Global Atmosphere (TOGA) Tr opical Atmosphere Ocean (TAO) buoy moorings over the equatorial Pacifi c Ocean and a bulk aerodynamic flux algorithm developed as a result of the TOGA Coupled Ocean-Atmosphere Response Experiment (COARE). It is shown that mesoscale enhancement is due primarily to the lack of wind steadiness on subsynoptic timescales and is associated with periods of significant precipitation. The magnitude of the mesoscale enhancement of monthly averaged sea surface evaporation is found to be similar to 10% or less of the total. During occasional periods with weak and var iable winds over the western Pacific warm pool and the other major pre cipitation zones in the equatorial Pacific, the mesoscale enhancement of monthly averaged evaporation can reach 30% of the total evaporation . A similar result is obtained for mesoscale enhancement of diffusive air-sea sensible heat transfer using data from TOGA TAO moorings. Howe ver, a comparison of results from the colocated TAO and Improved METeo rological measurements (IMET) moorings during TOGA COARE, and results previously reported from a pre-COARE cruise in the western Pacific war m pool region, indicate that processes in addition to mesoscale wind v ariability may be important contributors to the mesoscale enhancement of the sensible hear Aux. It is suggested that the most important effe cts of atmospheric mesoscale systems on tropical ocean evaporation and sensible heat flux are represented in existing climatologies.